The present invention relates in general terms to an expandable tubular device for implantation in the lumen of a body duct in order to ensure a passage therein.
This invention applies mainly to the field of the treatment of blood vessels exhibiting stenoses, and more generally to the field of the treatment of diseases of various anatomical ducts of the human or animal body, such as, for example, the urinary ducts, especially the urethra, or else the digestive ducts, especially the esophagus.
The percutaneous implantation of an expandable tubular device, commonly designated by the American term stent, in a stenotic blood vessel is generally recommended, for example after a conventional angioplasty, for preventing the dilated vessel from closing up again spontaneously or for preventing its occlusion by the formation of a new atheromatous plaque and the possible recurrence of stenosis.
Document EP 0540290, in particular, discloses an expandable tubular device in the form of a stent; in general terms it consists of an assembly of radially expandable, tubular elements aligned along a common longitudinal axis and successively joined together in pairs by a plurality of linking members.
Each of the above-mentioned tubular elements consists of a strip forming a zigzag corrugation defining bent extreme portions which are successively connected together in pairs in opposite directions by rectilinear intermediate portions.
As can be seen, by virtue of this zigzag conformation, such a device is expandable between a first, constricted state, enabling it to be implanted percutaneously by means of an insertion device of reduced diameter, and a second, expanded state, in which said device makes it possible to ensure a passage in the lumen of the body duct.
The expandable device described in said document of the prior art is inserted by means of an angioplasty balloon-tip catheter.
For this purpose said device is placed in the constricted state on the balloon, the latter being inflated at the point of release in order to cause said device to dilate.
It has been observed that the expansion of the device described in the above-mentioned document does not occur uniformly, the symmetry of said device being in itself insufficient to distribute the deformation forces exerted thereon during the inflation of the balloon.
A particular consequence of the non-uniform expansion of the device described in the above-mentioned document, which is due especially to the absence of distribution of the radial forces exerted thereon, is that it does not allow a passage of constant dimensions to be obtained in the body duct, so this type of device is not entirely satisfactory.
Under these conditions the object of the present invention is to solve the technical problem consisting in the provision of a novel design of expandable tubular device which guarantees a uniform expansion, especially during the inflation of a balloon used to insert it, and a good distribution of the radial forces exerted thereon after its insertion, and which thus makes it possible to obtain a constant passage in the body duct to be treated.
The solution to this technical problem, according to the present invention, consists of an expandable tubular device for implantation in the lumen of a body duct, such as a blood vessel in particular, in order to ensure a passage therein, said device consisting of an assembly of tubular elements aligned along a common longitudinal axis and successively joined together in pairs by a plurality of linking members, each tubular element consisting of a strip forming a zigzag corrugation defining bent extreme portions which are successively connected together in pairs in opposite directions by rectilinear intermediate portions, wherein the thickness of said strip forming each of the above-mentioned tubular elements, measured radially relative to said tubular element, is greater than the width of this strip in said bent portions.
Thus, as can be seen, the novelty of the proposed solution lies in the fact that the distribution of the deformation forces during the expansion of the device is optimized by adjusting, at least in certain portions constituting each tubular element of the device, the thickness/width ratio as a function of the forces exerted thereon.
The fact that the thickness is relatively greater than the width in the above-mentioned bent portions actually makes it possible to favor a uniform expansion of the device, as it is precisely these zones which are subjected to the highest radial stresses during the inflation of the balloon.
Advantageously, to further optimize the distribution of the forces exerted on the device, both during its insertion and in the use position, the thickness of the strip forming each of the above-mentioned tubular elements will be less than the width of this strip in the rectilinear portions.
Again advantageously, the thickness of the strip constituting each tubular element is less in the rectilinear portions than in the bent portions, whereas the width of the strip constituting each of the above-mentioned tubular elements is greater in the rectilinear portions than in the bent portions.